Dinosaur eggs

Fossilised dinosaur eggs - their size and spherical shape suggest they came from a sauropod dinosaur.Image: Jon AugierSource: Museum Victoria

While the dinosaurs have been extinct for millions of years, there are clues that can help us to piece together how they reproduced. Evidence includes fossil eggs and nests and rare discoveries of embryonic skeletons and soft-tissue. Birds descended from theropod dinosaurs and crocodilians are related to dinosaur ancestors, so by looking at modern day animals we can make some informed guesses about how dinosaurs reproduced and looked after their young.

As far as we know, all dinosaurs laid hard-shelled eggs rather than giving birth to live young. Eggs belonging to most groups of dinosaurs have been identified, except those of the armoured stegosaurs and ankylosaurs. Identifying which dinosaur laid a particular egg is not always easy and there have been cases of mistaken identity.

Fossilised dinosaur eggs - their size and spherical shape suggest they came from a sauropod dinosaur.Source: Museum Victoria

Discovery of fossil eggs

The first dinosaur egg discoveries were made in France in the mid-1800s. Fossil eggs have since been discovered on every continent except Antarctica and Australia. The most spectacular finds include entire nesting grounds caught in sandstorms, floods and volcanic eruptions that rapidly buried the eggs and babies and fossilised them in their original positions.

In the early 1920’s, expeditions to the Gobi Desert in Mongolia led to the discovery of skeletons of Protoceratops associated with fossilised eggs in circular nests. The skeleton of a carnivorous dinosaur was discovered poised above one clutch of eggs, implying it was caught in the act raiding the nest for food, earning it the name Oviraptor (egg thief). It was later realised that these eggs were instead those of Oviraptor itself, and the skeleton was that of a brooding parent protecting her own eggs rather than stealing them to eat.

Spectacular discoveries of dinosaur nest sites of hadrosaurs and theropods have been uncovered in north-western USA and southern Canada. These hadrosaur nests provided the first evidence of parental care among dinosaurs, and led to the naming of one genus as Maiasaura, meaning ‘good mother lizard’.

The largest known dinosaur nesting site was discovered at Auca Mahuevo in Argentina in the 1990s. Here thousands of clutches of eggs from a vast sauropod hatchery were buried in mud after a flood in the Cretaceous period. Some of these fossil eggs contain preserved embryos with skin impressions.

Dinosaur nesting behaviour

Just as different types of birds show varying degrees of care for their eggs and young, it is likely dinosaurs did the same, using different strategies in nest construction, incubation and parental care.

Evidence from the Auca Mahuevo site suggests that Sauropods laid 20-40 eggs into a simple depression in sand. They nested in groups, with hundreds of animals producing nests close together. There is no evidence of burial in sand or vegetation so they may have relied on the heat of the sun to incubate the nests. While it is possible that the adults protected the nesting area, the closely packed clutches make it unlikely that parents tended individual nests.

The hadrosaur Maiasaura nested in large colonies with well-spaced nests; enough room for parents to tend to their offspring. Mothers laid 30-40 eggs in a raised circular bowl. They covered the incubating eggs with vegetation that heated the nest as it rotted. Like modern parrots, the newly hatched Maiasaura stayed within the nest and parents brought them food and protected them.

Theropods such as Troodon built dish-shaped nests with 16-24 eggs in a spiral pattern. Fossils of adult skeletons of theropods on top of egg-clutches suggest they directly sat on their nests, incubating them with warmth from their feathery bodies. As the shells of newly-hatched Troodon eggs show no evidence of trampling, the hatchlings were seemingly precocious, leaving the nest at a young age. They were probably able to disperse themselves quickly from the nest after hatching and were likely capable of feeding themselves, in the manner of baby chickens and crocodiles.

Shapes and sizes

Dinosaur eggs clearly came in a variety of shapes and sizes. Theropod eggs varied from long and elongate to teardrop-shaped, In contrast, many herbivorous dinosaurs had round, almost spherical eggs. Dinosaur eggshells were made of calcite with microscopic pores allowing the developing embryo to ‘breathe’.

Dinosaur eggs came in a variety of sizes. The smallest dinosaur eggs were just a few centimetres across. At the other end of the scale, sauropod eggs could be 30 cm long and 25 cm wide. Biggest of all are enormous 70 cm long eggs from a giant oviraptor from China.

Despite their impressive size, even the largest dinosaur eggs are small compared with the adults who laid them If the eggs were any larger, the eggshell would need to be very thick and would be impossible for sufficient air to diffuse through the shell. The shell thickness of such an egg would also be difficult for a hatchling to break.

Artist’s reconstruction of a hatchling ornithopod dinosaur emerging from an egg.Source: Artist: Peter Trusler / This material has been reproduced with the permission of the Australian Postal Corporation. The original work is held in the National Philatelic Collection.

Further Reading

Chiappe, L. M. and Dingus, L. 2001. Walking on eggs: the astonishing discovery of thousands of dinosaur eggs in the badlands of Patagonia. Scribner Publishing

Comments (41)

I believe I have found a dinosaur egg. It's the right shape and size. And it appears to have an egg shell that is mostly intact. I live in the Bristol TN area. Is there some place local where I can have this item checked out?

Hi Teresa - That sounds like an interesting find! The East Tennessee State University seems to be not far from you, and they look like they have an active Palaeontology Department. I would start there, and perhaps they can recommend other useful resources.

David
27 November, 2010 15:58

I have just purchased what appears to be a dino egg. I live in West Palm Beach, FL. Is there a location I can take it to that may be able to identify it. Thank you. David

Hello! I have a rather large round stone that I believe is to be considered a dinosaur egg. My grandmother handed me down many arrow heads, petrified shark teeth, old pipes, etc.. when my grandfather passed away. I also have in my posession what is supposed to be a wooly mammoth bone. Where can I go in Grand Junction, CO to have these rarities checked out? Thank you!

Hi Damon; that sounds like quite a collection. Given Colorado is not too far from some world-famous fossil sites, you are quite well placed for Museums that will be able to help you, such as the Museum of Western Colorado. You can find out more at their website at http://www.museumofwesternco.com/visit/dinosaur-journey/

Good luck!

RENO
17 June, 2011 07:48

I THINK I FOUND A DINOSAUR EGG IN IMPERIAL, CA. HOW CAN I FIND OUT FOR SURE IF IT IS?

My son found an interesting "rock". It is an almost perfect egg shape,smooth, light beige, and has almost invisible holes all over. He found it amounst sea grass and some large rocks at a beach in Ma. Is it even possible to find a dinosaur egg in this area, intact, and in such great shape? If it is, do you have any idea what kind of dino came from this area and/or where to take it for more information? btw, its the size of a large chicken egg, maybe a little bit bigger. thx, Ps: my son is 11 and excited no matter what it is lol.

Reno and Kristina - without seeing the object, or even photographs, it is impossible to verify if either of your specimens are fossil eggs. Although, being an Australian Museum, we are not experts on your local geology, it is worth noting that neither Massachusetts nor California are known to yield fossilised eggs that I am aware of. We suggest you contact your nearest museums with expertise in natural history for specific advice on your specimens; be aware that theymay need to loan the material from you to examine it properly.

scott carnes
5 October, 2011 17:18

found dinosaur egss and other fossils in sault ste marie ontario canada who do i call ive compared it to your pics and many others seems real deal

Given your location, we recommend that you contact the American Museum of Natural History (AMNH) who may be able to assist you further. Their website has details on the AMNH Fossil Identification Service.

daniel winge
11 April, 2012 09:51

I think i have an amazing specimen of a dinosaur egg .i live in sioux falls SD. who can i contact to check it out. ?

Hi there Daniel, we specialise in Victorian dinosaurs, so it would be best for you to get advice from someone in your more immediate area. One good contact could be the University of Montana Palaeontology Centre, the staff at which might be able to help you further with you question.

Lisa knight
10 July, 2012 19:52

I think I found a dinosaur egg where can I go to check if it is a dinosaur egg.

I believe my aunt has tons fosilised dinasoar eggs on her property in Tn. I am from Indiana and heading home from a short visit there. She asked us to take some and see what we can find out about them. Where should we start? Also can you tell me if there is any value to them other than a remarkable piece of history?

Hi Angel, given you are in the USA, you might be best served by using the Fossil Identification Service of the American Museum of Natural History (AMNH), which you can access here.

Hope this is of some help!

Matt
2 April, 2013 14:43

I have a fossilized egg in omaha nebraska were would i take it to see if it is real? A friend said she seen one on vacation at a museum I just tought it was a rock it is still right next to the other rocks time to find out if it is real.

Hi I have what I think is a dinosour egg !! When I was a Kidd I went around Australia with my mum an dad.. I found a fossil witch looks a lot like a egg srounded in rock an I just want to know if it's the reall thing ... I live in Newcastle nsw Australia

My son found what he believes to be a dinosaur egg. The size and shape seem to be within what I have seen online but it is very heavy. How can we tell if it is real. He found it in California but we live in N. Nevada.

We have recently found an oval rock approximately 205mm x 140mm wide in a oval shape. Completely symetrical. Has what appears to have had an outer softish shell as a fossilised shell and other small small items are pressed into it. Has an orange ocre red interior. We found it approximately 5 to 6 meters down in a sedimentary lined cut through the ground. We were approximelty 500m from the ocean. About 100km from Albany on the WA south coast. Could it be a dinosaur egg.

I JUST MOVED TO KIMBERLING CITY MO. NEAR BRANSON MO. I'VE ALWAYS LOOKING FOR ROCKS THAT ARE UNUSUAL.
I FOUND SOME ROCKS THAT LOOK LIKE EGG'S FROM A DINOSAUR. I LOOKED THEM UP AND THEY LOOK LIKE THE PICTURES ON MY PHONE. CAN YOU TELL ME WHAT THEY MAY BE

Sorry we are unable to provide identifications from photos, you are best taking your specimens to the nearest museum that has palaeontology collections.

Travis Carron
4 September, 2014 06:58

I have a bunch of what I believe are dinosaur eggs that we found on a jobsite. They were embedded in bluff when we were doing some excavation I have 8 or 9 that I took home. The jobsite was in the southern st Louis Missouri area. Where can I go close to here that may be able to tell me more about them and if they are really dinosaur eggs!!

Hi Travis - given your location, the best option for you would be to contact the Saint Louis Science Center, who are likely to be much better placed to assist you with your specimen.

Skye McGeechan
1 November, 2014 17:33

I visited the museum and saw the dinosaur egg. I am doing my naturalist badge for scouts and I need to explain the egg but I can't remember how old it was. Can you please give me an idea of how old the dinosaur fossil eggs are>

Hello Skye - there are actually two seperate displays featuring real dinosaur eggs, one in the Dinosaur Walk exhibition as seen here, and the other in 600 Million Years: Victoria Evolves. Both are Mid-Late Cretaceous in age (90-65 Million Years Old).

Hope this helps, and good luck!

john berry
22 November, 2014 08:00

I found clutches of prehistoric petrified egg in the north kimberley area. Each nest 4 to 6 eggs.about 35 clutches in total.300 /350 mm in length.cracked one open its a egg.hope too here from you .